A digital copying machine, an example commercialized image forming apparatus, reads an original image by means of an image read section to process the read original image in a specified manner by means of an image processing section, and prints out the processed image data by means of a recording section as a copy image. Thus, the digital copying machine of this type produces an image on a sheet using only the image processing functions pre-installed therein.
On the other hand, an idea of forming a network by interconnecting a plurality of image recording apparatus or the like has been proposed recently. For example, Japanese Laid-Open Patent Application No. 116834/1978 (Tokukaisho 53-116834) discloses an arrangement to interconnect a plurality of image reading apparatuses and a plurality of image recording apparatuses through a single control section.
This arrangement enables each image recording apparatus to output a copy of an original image read by any of the above image reading apparatuses. Thus, when more than one kind of document is copied, each kind of document is set to a separate image reading apparatus and the copy is made by a single image recording apparatus, thereby reducing an idle time of the image recording apparatus compared with a case where each kind of document is set in a single image reading apparatus.
Also, Japanese Examined Patent Publication No. 36592/1995 (Tokukouhei 7-36592) discloses an image forming system including a plurality of copying machines interconnected through a single control apparatus, and each copying machine is furnished with an image read section and an image record section. In this system, image signals subject to recording are distributed to more than one copying machine according to a specified copying mode, so that those who received the image signals can carry out the copying operation in parallel.
However, the above conventional image forming systems has a number of problems.
To begin with, each image processing function of the digital copying machine depends on a software program, which has been developed at an increasing pace. Thus, the image processing function is upgraded in a short period and new models with additional functions have been steadily commercialized. Therefore, the state-of-the-art digital copying machine with desired image processing functions becomes an outdated model with relatively low level functions as soon as the user purchases it.
Because the user can neither upgrade the functions of his digital copying machine nor simply add new functions, if he wants higher level or new functions, he has to purchase a new model. This is an economic burden for the user and a manufacturers' problem accompanying with their efforts in always meeting users' demands.
The same can be said about a memory capacity of the digital copying machine. To be more specific, most of the higher level image processing functions, such as an electronic RDH (Recycle Document Handler) function, are feasible only when the digital copying machine has a large memory.
A possible solution to the above problem would be interconnecting copying machines through a transmitting apparatus to enable them to share their memories, a practical arrangement of which, however, has not been discussed in any of the prior art documents.
In addition, suppose that a first copying machine requests a second copying machine to store the transmitted data on its behalf, then, the second copying machine eventually accumulates a great volume of image data for a considerable period unless the first copying machine issues a return request of the image data. Thus, the memory of the second copying machine is occupied by the image data from the first copying machine. This limits the memory function of the second copying machine, in other words, this causes an insufficient memory at the second copying machine's end, thereby hindering the full performance of the second copying machine.